1. Field of the Invention
This invention relates to slip forms, in general, and, more particularly to slip forms for the construction of manhole and water pipe collars, in particular.
2. Description of the Prior Art
Presently, manhole assemblies are generally constructed of a precast cylindrical barrel, with top opening, the barrel provided at its base with ports for connecting to existing sewer lines; a precast manhole cone placed upon the barrel; a series of precast riser rings of varying heights, placed upon the cone to bring the manhole assembly to a desired height relative to a road surface; and finally a precast manhole ring, of standard height, placed upon the risers to bring the manhole ring to a proper height for placement of a manhole cover therein. The top of the manhole ring is generally positioned one-quarter of an inch below the top of the road surface, which is generally constructed of asphalt or concrete. An annular void is left about the risers and ring for the pouring of a concrete collar to present a nearly flush surface with the surrounding road surface.
In the precast risers and manhole ring are provided in standard heights, an exact elevation cannot be achieved using the precast products and therefore it is common to use small spacer blocks between risers or between risers and ring to bring the assembly to an exact height. Such construction is time consuming; expensive in the provision of precast rings; and is time consuming to the construction crew, often requiring grout to be placed between overlying riser rings and between riser rings and the manhole ring.